1. Field of the Invention
This invention relates generally to chemical mechanical planarization or polishing tools and, more particularly, to a method and apparatus for chemical mechanical polishing of a semiconductor wafer with a polishing pad having controlled release of desired micro-encapsulated polishing agents.
2. Discussion of the Related Art
In semiconductor device manufacturing of very large scale integrated (VLSI) circuits, extremely small electronic devices are formed in separate dies on a thin, flat semiconductor wafer. In general, various materials which are either conductive, insulating, or semiconducting are utilized in the fabrication of integrated circuitry on semiconductor wafers. These materials are patterned, doped with impurities, or deposited in layers by various processes to form integrated circuits. VLSI integrated circuits include patterned metal layers which are generally covered with dielectric materials, such as oxide, followed by a subsequent metalization, etc. The semiconductor wafers thus contain metalization layers and interlevel dielectrics.
Increasing circuitry miniaturization and a corresponding increase in density has resulted in a high degree of varying topography being created on an outer wafer surface during fabrication. It is often necessary to planarize a wafer surface having varying topography to provide a substantially flat planar surface. One such planarization process known in the art is chemical-mechanical polishing (CMP).
Chemical mechanical polishing or planarization has been widely used in the semiconductor industry for smoothing, polishing or planarizing coating or layers on the surface of semiconductor wafers. This process has been used to achieve the planarization, the controlled reduction in thickness, or even the complete removal of such layers which may include, for example, an oxide on the surface of the semiconductor wafer. Apparatus for such chemical mechanical polishing process is well known and used in the semiconductor industry and is currently commercially available.
Briefly, the chemical mechanical polishing process requires that a workpiece be held, with a desired coated surface face down, on a polishing pad supported on a rotating table, in the presence of an abrasive slurry. A chemical mechanical polishing machine can include a single rotating polishing plate and a smaller diameter rotating wafer carrier to which a wafer (or wafers) is (are) mounted. The wafer carrier is held above the polishing plate, either in a stationary fixed position or oscillating back and forth in a predetermined path in a horizontal plane, while both polishing plate and wafer carrier are rotated about their respective center axes. A slurry, consisting of an abrasive suspension with or without an etching reagent, is fed onto the polishing plate during polishing of the wafer. The slurry, also referred to as a carrier liquid, can be selected to include an etchant for the coating being planarized and for not substantially attacking other materials involved in the process. The slurry is further fed between the polishing plates to polish and flush away the material removed from the semiconductor wafer.
One problem with CMP is that it is difficult to deliver certain fluid media agents to the surface of a substrate during chemical-mechanical polishing. In a typical CMP apparatus, the substrate surface being polished is in intimate contact with an abrasive cloth, also referred to as the polishing "pad", under pressure, and while immersed in an abrasive chemical medium, referred to as the "slurry". In addition, the abrasive cloth and wafer are both in motion. The problem is how to deliver special fluid phase agents to the substrate surface being polished, under these conditions. In many cases, the desired agents are also not compatible with the slurry environment and cannot co-exist in any pH slurry medium. This difficulty may be extended to include such other agents as: reactive chemicals, polar or non-polar fluids, immiscible fluids, or other agents which would not maintain their desired properties or are incompatible if dispersed in a slurry, but which are desirable agents in the polishing process.
Furthermore, in semiconductor wafer polishing, the delivery of fluid polishing agents to the wafer surface is impeded by the juxtaposition of wafer and polishing pad surfaces so as to exclude all but a thin hydrodynamic layer of fluid. As the applied mechanical polishing forces are increased, the polishing rate initially increases, then begins to decline due to the increasing difficulty of delivering reactive polishing fluids to the wafer surface.
It would thus be desirable to provide a method and apparatus for delivering certain fluid media agents to the surface of a substrate during chemical-mechanical polishing.